(1) Field of the Invention
The present invention relates to apparatus and methods for sensing and monitoring traffic, particularly, although not exclusively, road-traffic. For example, the invention may also be applied to the sensing and monitoring of rail traffic or aircraft on runways.
(2) Description of the Art
The ability to sense and monitor motor vehicles on a length of road or a length of a lane of a multi-lane highway is useful as it allows detection of congested portions of road. Such detection allows drivers to be given advance warning of such portions, preventing further traffic build-up. If the sensing and monitoring is sufficiently detailed, such detection also allows authorities to make appropriate use of available road resources. For example, when lanes of a portion of motorway become congested, the hard-shoulder may be made available for ordinary use by motorists. In the long-term, detailed information on traffic density is useful in long-term planning of upgrading or improving existing roads and building new ones.
At present, apparatus for sensing and monitoring road traffic provides only sparse information concerning traffic conditions along roads due to the expense and limited range of current traffic sensing and monitoring apparatus. CCTV systems only provide clear views of traffic over distances of approximately 50 m. Inductive loop sensors can only provide information at a point and are generally only installed in roads using a relatively large separation (e.g. 500 m) between consecutive sensors because a higher linear density of sensors is prohibitively expensive. This is because each inductive loop sensor requires individual processing electronics and a power supply. These types of apparatus can only provide the type of detailed information required for efficient road management if they are installed at frequent intervals and therefore high cost. Installation of these systems at frequent intervals also gives rise to high maintenance costs due to the employment of large amounts of hardware. In the case of inductive loop sensors there is an additional problem of high installation costs associated with frequent installation.
Current traffic sensing and monitoring apparatus can only provide a high level of traffic information per unit of road length together with high purchase, installation and maintenance costs.